abcnews.go.com
Slithery Invader
Florida Ecologists Use to
Electric Shocks to Reduce
Number of Exotic Eels
The Asian swamp eel measures up to 3
feet in length, has two beady eyes and
can survive for months without food.
(www.biology.usgs.gov)
By Amanda Onion
Sept. 28 — When John Curnutt first netted a catch
of Asian swamp eels and dumped the slithery,
brown, tubelike creatures into a bucket, he knew
Florida was facing an unusually fierce invader.
“Usually the fish we capture calm down after sitting in
the bucket in warm
weather,” says Curnutt,
a research ecologist at
the Florida biological
division of the U.S.
Geological Survey.
“These eels just kept
flopping. We finally had
to pour a chemical in the
bucket to kill them.
They’re solid muscle.”
Savored and
Feared
In China and Japan, the
Asian swamp eel, also
known as the rice eel, is
a delicacy. Sometimes
called unagi when it’s on
the table, the eel is
eaten pickled, with sweet
sauces, grilled on a stick
and broiled over rice,
and other variations. Not
surprisingly, the
muscular fish is prized in
China for its
stamina-lending
properties.
But in Florida,
appetites for the
3-foot-long eel are rare. Indeed, the creature, introduced as
an exotic species sometime in the early to mid-1990s, is
doing very well near the top of the food chain.
That’s worrisome to ecologists, who fear the species
could suck up food supplies of native fish and wading birds in
Florida’s 1.4 million-acre Everglades National Park. No one is
sure how the eel first arrived in the state, but Curnutt
suggests it may have been released by someone who had
tried to raise the species on a fish farm.
Although the eels have not reached the interior of the
Everglades park, their numbers are dense — possibly in the
tens of thousands — just around its borders, in nearly 55
miles of outlying canal systems. Populations of the eel have
also been found in Hawaii, north of Miami and in southern
Georgia.
Some fear the extremely mobile and hardy eel could
spread even further. Leo Nico, the first USGS biologist to
discover the eel in Florida, believes it could eventually
penetrate large portions of the United States if left
unchecked.
The problem is finding a way to stop it.
Indestructable Invader?
The eel doesn’t appear to be affected by most fish poisons.
Biologists are prevented from using stronger ones, such as
cyanide, since the canals around the park are linked up with
a Florida aquifer.
It’s nearly impossible to hunt down the eels by hand and
net since they’re mostly nocturnal and can take quick shelter
in crevices. Exploding dynamite in the water, a technique
that kills most fish by popping blood vessels in their air sacs,
doesn’t work with eels because they have no such organ.
Draining ditches is no solution, either, since the eels can
survive in water and on land.
Even encouraging people to eat the animal — like
authorities in Louisiana have done to reduce numbers of the
swamp rat, or nutria — poses risks. The Asian swamp eel
bears some resemblance to the darker American eel, whose
numbers are dangerously low.
“Each creature presents its own kind of soap opera when
it’s introduced, depending on its behavior and the timing of
its introduction.” says Carole Goodyear, a biologist at the
National Marine Fisheries Service who recently authored a
survey of unwanted species in the United States.
The Asian eel’s soap opera, so to speak, is its
adaptability. The Asian import is equipped with both gills and
lung-like organs to breathe. It can survive in marshes and
swamps, as well as in ponds, canals, roadside ditches and
rice fields. If conditions become dry, the eel simply slithers
into mud or grass and can live there for as long as seven
months with no food.
USGS biologists have settled on a rather extreme
approach for controlling the thriving fish — electric shocks.
Shocked Out of Water
In a little over a month, teams of biologists from the USGS,
the Florida Game and Freshwater Fish Commission and
Florida International University will set off in boats equipped
with some lethal machinery. Each boat will carry an 800-volt
generator and two metal arms that can be lowered into the
water. When a current is run between the two prongs in the
water, everything within about two feet of its reach will
receive a big shock.
While most fish quiver, or swim to the bottom at such a
shock, eels react more dramatically.
“It makes them crazy,” says Curnutt. “They shoot up out
of the water and then we catch them with nets.”
By shocking and capturing eels from a range of locations
throughout southern Florida, the team hopes to compile a
thorough survey of the eel’s numbers and locations. Armed
with that information, the plan is to go ahead with a targeted
attack on the eels, possibly using poisons.
Why go to so much trouble over a single breed of fish?
One reason is it’s a tenacious predator. To eat its prey,
which Curnutt has observed includes “almost anything” from
frogs to small fish to shrimp to turtle eggs, the eel uses its
mouth as a vacuum cleaner and sucks in smaller creatures.
Those that it can’t suck in, it grabs with its teeth and spins
quickly until they are torn in half and can be ingested in
smaller chunks.
“The concern is the space they take up as predators
means they’re replacing another native creature in the food
chain,” says Paul Shafford, head of non-native fish research
at the Florida Fish and Wildlife Conservation Commission.
“They change the energy flow of the ecosystem.”
Uncertain Effect
Still, Shafford is quick to point out that adding an animal to
the food chain doesn’t always have a dire impact on an
ecosystem.
“We don’t know yet is if the eel’s entry into the aquatic
ecosystem is detrimental, innocuous or even valuable,” he
says.
Shafford notes that at least one exotic fish species in
Florida’s waters has proven helpful. The imported butterfly
peacock bass has preyed upon and reduced populations of
another unwanted exotic fish by 25 percent. The exotic bass
has also proven a favorite of anglers who provide Florida
with a multimillion-dollar fishing industry.
But Curnott argues the Asian eel may be an exceptional
threat.
Florida’s warm, wet climate is known for accommodating
outside species — 28 fish from Central America, Africa and
Asia now thrive in its waters. Curnutt notes almost none has
managed to reach the deep interior of the Everglades park.
Most fish, he explains, get stuck in marsh land and expire
before reaching the interior.
That’s where the Asian eel has a clear advantage.
“This eel can burrow in the mud and wait for months and
then get going again,” he says. “As an adaptable predator, it
has the potential to colonize the whole system.” |
